1. Field of the Invention
This application relates to a truck brake system, and more particularly to an apparatus and method of forming an inexpensive sensor for monitoring wheel speed rotation.
2. Discussion of the Art
Although a number of new technologies exist for detecting rotation to determine wheel speed, none are presently believed to be viable alternatives due to cost of application of the new technology. For example, consideration has been given to detecting rotation by using optics or infrared sensors. To date, these alternatives are deemed to be too expensive. Moreover, the use/operation of optical arrangements is sensitive to the external environment, i.e., mud, dirt, etc.
The established technology senses wheel speed based on variable reluctance. That is, a tone ring rotates with the wheel. Mounted adjacent to the tone ring is a pickup or sensor. The sensor includes a pole piece disposed closely adjacent to the tone ring so that it is sensitive to movement of the ring. The pole piece cooperates with a magnet to establish a magnetic field that is interrupted by rotation of the tone ring. The tone ring has teeth that interrupt the flux path and the this causes a signal in the sensor which is communicated to the winding which amplifies the signal. In addition, a flux concentrator, typically a mass or block of metal, is also used to improve the efficiency of the sensor.
A separately manufactured plastic bobbin is used in the wheel speed sensors in commercial use today. The winding is received around the bobbin and the winding is secured to an electrical connector extending outwardly from an end of the sensor remote from the tone ring. A number of different shaped connectors or tails are used. For example, a straight head, right-angle head, or a straight head with an integrated shoulder are three types of molded connector boots or shrouds requiring separate molds for each of the different shapes. This wide variety of configurations is less cost efficient than a standardized design. Accordingly, needs exist in improving existing technology, with desired improvements in both cost and efficiencies of performance.
The present invention provides a wheel speed sensor that is significantly reduced in cost and obtains improved signal efficiencies, while maintaining the flexibility of design.
An exemplary embodiment of the wheel speed sensor includes a one-piece pole and magnetic flux concentrator having molded regions over first and second ends with a winding received between the first and second molded materials. A magnet is received over the pole and preferably encased within the first material to establish a magnetic field. A sleeve is received over the assembly allowing the pole to extend outwardly from the first end of the sleeve and a connector assembly from the second end.
The one-piece pole and magnetic flux concentrator includes first, second, and third regions or sections having different cross-sectional dimensions. The first or smallest section serves as the pole piece of the sensor, the second section serves as an internal support for the winding, and the third section has the largest cross-sectional dimension and serves as the flux concentrator.
An exemplary method of assembling the wheel speed sensor includes the steps of providing a one-piece pole and magnetic flux concentrator, mounting a magnet over a first end, molding a first material over the magnet and first portion of the magnetic flux concentrator; molding a second material over a second portion of the pole and magnetic flux concentrator, winding a wire about the pole and magnetic flux concentrator between the first and second materials, and enclosing the assembly.
A sleeve is dimensioned for receipt over the first and second materials and is mechanically secured thereto.
Electrical connection is completed from the windings to a plastic overmolded electrical connector that is inserted in one end of the sleeve.